1. Field of the Invention
This invention relates to a prosthetic joint and, more particularly, to a prosthetic hip joint which prevents particulate debris generated from the joint from entering the body cavity and prevents debris from the body cavity entering the joint.
2. Art Relating to the Invention
Prosthetic joints are well-known devices and, in the case of a hip joint, comprise an acetabular component which is affixed to the acetabulum, i.e. hip bone, and a femoral component, affixed to the femur bone. The acetabular component comprises a socket which is affixed to the acetabulum and a ball that rotates within the socket. The femoral component comprises a stem which is affixed to the femur and a neck which is affixed to the ball. Typically, the socket is divided between an outer cup that faces the acetabulum and an inner cup that faces the ball. The inner cup of such joints is typically made of polyethylene while the outer cup is made of a metal alloy or a ceramic material. The ball is made of a metal, metal alloy or ceramic material.
One of the problems associated with prosthetic joints is wear debris, namely polyethylene wear debris generated from the interface between the ball and the socket and the interface between the inner cup and the outer cup. This wear debris finds its way into the human cavity and causes inflammation. Inflammation can cause bone destruction as well as weakening of the bond between the prosthesis and the bone.
Another problem is body debris generated from the body cavity finding its way into the joint and interfering with the joint. Body debris such as bone pieces can find their way into the joint and cause excessive wear or damage to the joint.
To prevent debris from leaving the junction between the outer cup and the acetabulum and the junction between the stem and the femur, it has been suggested that a barrier or capsule be placed over each of these junctions, see U.S. Pat. No. 5,735,900. It has also been suggested that a barrier or capsule extend over only the junction between the stem and the femur bone, see U.S. Pat. Nos. 5,899,942 and 6,132,470.
For preventing debris from leaving the interface of the ball and the socket, it has been suggested to employ a flexible capsule which extends from the ball where it affixes to the stem to the outside of the socket where it is affixed to the hip bone, see U.S. Pat. Nos. 3,739,403; 4,731,088; 4,822,368; 5,514,182; 5,702,483; and 5,755,807.
Typically, a prosthetic hip joint comes in different size sockets, balls and stems, all of which are separate and all of which are selected and assembled by the doctor during the replacement operation. The selection is based on the size of the patient.
Typically, the doctor, during the operation performs the following steps in sequential order: selects an inner cup, an outer cup, a ball and a stem; affixes the outer cup to the hip bone; affixes the inner cup to the outer cup; affixes the stem to the femur; affixes the ball to the stem; and finally, places the ball in the socket. If a capsule is used, the capsule is set in place at the very end.
As will be appreciated, so many different sized parts which must be assembled during the operation increase the duration and complexity of the operation. Also, because the capsule is affixed at the end of the assembly, it may not be strongly adhered.
It has now been discovered that debris contamination problems can be solved by employing a preformed ball and socket with a capsule already attached thereto. Such a preformed unit is assembled at the factory rather than by the doctor in the operating room.
Additionally, by employing an already preformed encapsulated ball and socket, the time and complexity of the operation is also reduced.
Such a preformed acetabular component comprising a ball-socket-capsule unit means that the manufacturer makes the preformed unit with different sized sockets and different sized balls. Thus, the doctor need only size the socket and the stem to the patient""s bone structure. The step of assembling the socket, matching the ball and the socket and affixing the capsule between the ball and the socket has already been performed by the factory. This increases the strength of the bond between the capsule and the ball and socket as well as simplifies the overall operation.
Broadly, the present invention is an improvement in a prosthetic hip joint, wherein the improvement comprises:
a preformed acetabular component comprising:
(1) a socket adapted for attachment to an acetabulum;
(2) a ball with a first attachment member, said ball rotatably positioned within said socket, said first attachment member facing outward away from said socket; and
(3) a flexible joint capsule attached to said ball adjacent said first attachment member and to said socket, said capsule preventing wear debris from escaping from a joint between said ball and socket and preventing body debris from entering said joint and said capsule attached to said socket so as to avoid interference between the attachment of said socket to said acetabulum.
In the case of total hip replacement, the present invention further comprises:
a femoral component having a stem for attachment to a femur, and a second attachment member that mates with said first attachment member wherein said preformed acetabular component is attached to said femoral component by mating said first and second attachment members. Preferably, the mating of the first and second attachment members occurs after said preformed acetabular component has been affixed to an acetabulum and said femoral component has been affixed to a femur.
The capsule isolates the joint cavity and prevents debris from the ball and socket from entering the body cavity. Also, the capsule prevents body debris from entering the joint and causing damage to the joint.
Also, because the capsule is formed on the ball and socket in the factory rather than in the operating room, a very strong seal is made between the capsule and the ball and socket. As such, it provides strength to the ball and socket joint itself, thereby helping to prevent dislocation of the joint itself.
Also, the capsule can prevent body debris such as body fragments (like the ones which are produced during surgery), or cement debris, or metal debris from entering the ball and socket interface. It is known that if polyethylene is used to make the inner cup and the inner cup is scratched by such body debris, wear of polyethylene will progress faster than normal.
Furthermore, the space defined by the capsule and the ball and socket can be filled with different types of fluids to promote ease of movement between the ball and the socket, to prevent entrapment of the capsule in the joint between the ball and the socket, and to provide a self-healing or repair mechanism to the joint.
In surface replacement type hip prosthetics, the ball has a peg which is affixed directly into the femur bone. The top of the femur bone is cut to mate with the ball and drilled to accommodate the peg. In surface replacement type hip prosthetics, the peg is part of the ball. For surface replacement type hip prosthetics made in accordance with the present invention, the peg forms the first attachment member. Alternatively, if the ball has a cup section which surrounds the femur bone, then this cup forms the first attachment member.
Preferably, the socket has an inner and an outer cup and the capsule is affixed to either the inner or the outer cup. Where the socket has both an inner and an outer cup, the capsule also prevents debris from entering or leaving the joint between the inner and outer cup when the capsule is affixed to the outer cup.